Rotating field inductive data telemetry and power transfer in an implantable medical device system

Abstract

An improved implantable medical device system having dual coils in one of the devices in the system is disclosed. The dual coils are used preferably in an external device such as an external controller or an external charger. The dual coils are wrapped around axes that are preferably orthogonal, although other non-zero angles could be used as well. When used to transmit, the two coils are driven (for example, with FSK-modulated data when the transmitting data) out of phase, preferably at 90 degrees out of phase. This produces a magnetic field which rotates, and which reduces nulls in the coupling between the external device and the receiving coil within the implanted device. Moreover, implementation of the dual coils to transmit requires no change in the receiver circuitry of the implanted device. Should the device with dual coils also receive transmissions from the other device (e.g., the implanted device), the two coils are used in conjunction with optional receiver circuitry which likewise phase shifts the received modulated data signals from each coil and presents their sum to typical demodulation circuitry.

1 . An external device useable to transfer power or data to an implantable medical device, comprising:
 transmitter circuitry, wherein the transmitter circuitry produces a signal to drive two coils, wherein the two coils are wrapped around axes oriented at a non-zero angle with respect to each other,   wherein the signal is phase shifted at one of the coils when compared to the other coil to produce a rotating magnetic field for transferring the power or data to the implantable medical device.   
     
     
         2 . The device of  claim 1 , wherein the angle of the phase shift is approximately 90 degrees. 
     
     
         3 . The device of  claim 1 , wherein each of the coils is coupled to a tuning capacitor. 
     
     
         4 . The device of  claim 1 , wherein the magnetic field rotates around a first axis. 
     
     
         5 . The device of  claim 4 , wherein the first axis is orthogonal to the axes around which the two coils are wrapped. 
     
     
         6 . The device of  claim 1 , wherein the signal comprises a modulated data signal. 
     
     
         7 . The device of  claim 6 , wherein the modulated data signal is modulated using a Frequency Shift Keying protocol. 
     
     
         8 . The device of  claim 1 , wherein the two coils are coupled to receiver circuitry to receive a wireless broadcast from the implantable medical device. 
     
     
         9 . A method for transferring power or data from an external device to an implantable medical device, comprising:
 generating an oscillating driving signal;   splitting the driving signal to produce a first and a second driving signal, wherein the phase shift between the first and second driving signal is approximately 90 degrees;   applying the first driving signal to a first coil in the external device, and applying the second driving signal to a second coil in the external device, wherein the first and second coils are wrapped around axes that are approximately orthogonal to each other.   
     
     
         10 . The method of  claim 9 , wherein each of the coils is serially connected to a tuning capacitor. 
     
     
         11 . The method of  claim 9 , wherein the magnetic field rotates around a first axis which is orthogonal to the axes around which the two coils are wrapped. 
     
     
         12 . The method of  claim 9 , wherein the signal comprises a modulated data signal. 
     
     
         13 . The method of  claim 12 , wherein the modulated data signal is modulated using a Frequency Shift Keying protocol. 
     
     
         14 . A system, comprising:
 an implantable medical device; and   an external device,   wherein either the implantable medical device or the external device comprises transmitter circuitry for wirelessly broadcasting to the other of the implantable medical device or the external device, wherein the transmitter circuitry comprises:
 two coils, wherein the two coils are wrapped around axes oriented at a non-zero angle with respect to each other; and 
 transmitter circuitry, wherein the transmitter circuitry produces a signal to drive each of the coils, 
 wherein the signal is phase shifted at one of the coils when compared to the other coil. 
   
     
     
         15 . The system of  claim 14 , wherein the non-zero angle comprises a 90 degree angle. 
     
     
         16 . The system of  claim 14 , wherein the signal is phase shifted by approximately 90 degrees. 
     
     
         17 . The system of  claim 14 , wherein each of the coils is coupled to a tuning capacitor. 
     
     
         18 . The system of  claim 14 , wherein the magnetic field rotates around a first axis. 
     
     
         19 . The system of  claim 14 , wherein the signal comprises a modulated data signal. 
     
     
         20 . The system of  claim 14 , wherein the two coils are further coupled to receiver circuitry to receive a wireless broadcast from the other of the implantable medical device or the external device. 
     
     
         21 . An external device for receiving data transmitted from an implantable medical device, comprising:
 two coils for receiving a wireless modulated data signal from the implantable medical device, wherein the two coils are wrapped around axes oriented at a non-zero angle with respect to each other, wherein a first of the two coils produces a first signal and wherein a second of the two coils produces a second signal;   a summer for adding the first and second signals, wherein the first signal is phase shifted at the summer when compared to the second signal; and   demodulation circuitry coupled to the output of the summer.   
     
     
         22 . The device of  claim 21 , wherein the angle of the phase shift is approximately 90 degrees. 
     
     
         23 . The device of  claim 21 , wherein the non-zero angle is approximately 90 degrees. 
     
     
         24 . An external device useable to transmit data to and receive data from an implantable medical device, comprising:
 a first coil and a second coil, wherein the two coils are wrapped around axes oriented at a non-zero angle with respect to each other;   transmitter circuitry coupled to the first and second coils, wherein the transmitter circuitry produces a first modulated signal to drive the first and second coils, wherein the first modulated signal is phase shifted at the first coil compared to the second coil; and   receiver circuitry coupled to the first and second coils, wherein the first coil produces a second modulated signal and the second coil produces a third modulated signal, wherein the receiver circuitry processes the second and third modulated signals, wherein the second modulated signal is phase shifted in the receiver circuitry with respect to the third modulated signal.   
     
     
         25 . The device of  claim 24 , wherein the non-zero angle is approximately 90 degrees.